Method of producing all skin rayon



United States Patent METHOD OF PRODUCING ALL SKIN RAYON Byron A. Thumm,Swarthmore, Pa., assignor to American Viscose Corporation, Philadelphia,Pa., :1 corporation of Delaware N0 Drawing. Original application June29, 1955, Serial No. 518,932, new Patent No. 2,840,448, dated June 24,1958. Divided and this application July 26, 1957, Serial No. 674,292

'1 Claim. (Cl. 106-165) This invention relates to the production ofshaped bodies of regenerated cellulose from viscose and moreparticularly to filaments and fibers of regenerated cellulosefromviscose.

In the conventional methods of producing shaped bodies of regeneratedceilulose from viscose, a suitable cellulosic material such as purifiedcotton linters, wood pulp, mixtures thereof, and the like is firstconverted to an alkali cellulose by treatment with a caustic sodasolution and after shredding the treated cellulose material, it isallowed to age. The aged alkali cellulose is then converted to aXanthate by treatment with carbon disulfide. The cellulose Xanthate issubsequently dissolved in a caustic soda solution in an amountcalculated to provide a viscose of the desired cellulose and alkalicontent. After filtration, the viscose solution is allowed to ripen andis subsequently extruded through a shaped orifice into a suitablecoagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscosesolution is extruded through a spinneret into a coagulating andregenerating bath consisting of an aqueous acid solution containing zincsulfate. The filament may subsequently be passed through a hot aqueousbath where it is stretched to improve its properties such as tensilestrength. The filament may then be passed through a dilute aqueoussolution of sulfuric acid and sodium sulfate to complete theregeneration of the cellulose, in case it is not completely regeneratedupon leaving the stretching stage. The filament is subsequentlysubjected to washing, purification, bleaching, possibly other treatingoperations and drying, being collected either before or after thesetreatments.

The filaments as formed by the conventional methods, consist of a skinor outer shell portion and a core portion with a sharp line ofdemarkation between the two. The

' crenulated exterior surface when even small amounts of zinc salts orcertain other polyvalent metal salts are present in the spinning bath.The skin and core portions of the filament represent differences instructure and these different portions possess difierent swelling andstaining characteristics, the latter permitting a ready identificationof skin and core. The sharply irregular and crenulated surface structurehas a relatively low abrasion resistance and readily picks up foreignparticles such as dirt. Although the core portion possesses a relativelyhigh tensile strength, it has a low abrasion resistance and a lowflexlife, is subject to fibrillation and is relatively stiff.

It has now been discovered that the presence of small amounts ofmonoaminopyridine in the viscose, in the spinning bath, or in both theviscose and the bath results in the production of shaped bodies ofregenerated cellulose such as filaments, films, sheets and the likecomposed of all skin and having improved properties and characteristicsproviding that the amount of monoaminopyridine in maintained withincertain limits and the composition of the spinning bath is maintainedwithin certain composition limits which will be defined hereinafter. Themost readily distinguishable characteristic as compared to comventioiial filaments include a smooth, non-crenulated surface and thefilaments consist entirely of skin. All of the monoaminopyridines aresatisfactory, that is, 2-, 3- an l-aminopyriuiiie may be employed.

Where the monoaminopyridine is to be added to the viscose, the amountwhich is incorporated in viscose must be at least about 0.75% by weightof the cellulose in the viscose and may vary up to about 2.5% to 3%,preferably, the amount varies from about 1% to 2%. Lesser amounts do notresult in the production of products consisting entirely of skin andgreater amounts affect adversely the physical properties of theproducts. Amounts within the preferred range are most eirective inenhancing the characteristics and properties of the products. Theirionoarninopyrioine may be added at any desired stage in the productionof the viscose sucn as in the preparation of the refined wood pulp forthe manufacture of viscose, before or during the shredding of the alkalicellulose, to the xanthated cellulose while it is being dissolved in thecaustic solution or to the viscose solution before or after filtration.The monoaminopyridine is preferably added after the cellulose xanthatehas been dissolved in the caustic solution and prior to filtration.

The viscose may contain from about 6% to about 8% cellulose, theparticular source of the cellulose being selected for the ultimate useof the regenerated cellulose product. The caustic soda content may befrom about 4% to about 8% and the carbon disulfide content may be fromabout 30% to about 50% based upon the weight of the cellulose. Themodified viscose, that is, a viscose containing the small amount ofmonoaminopyridine, may have a sodium chloride salt test above about 7and preferably above about 9 at the time of spinning or extrusion.

in order to obtain the improvements enumerated hereinbefore, it isessential that the composition of the spinning bath be maintained withina well defined range. The presence of the monoaminopyridine in theviscose or in the spinning bath combined with these limited spinningbaths results in the production of yarns of improved properties such ashigh tenacity, high abrasion resistance, high fatigue resistance andconsisting of filaments composed entirely of skin.

Generically, and in terms of the industrial art, the spinning bath is alow acid-high zinc spinning bath. The bath should contain from about 10%.to about 25% sodium sulfate and from about 3% to about 15% Zincsulfate, preferably from 15% to 22% sodium sulfate and about 80 C.,preferably between about 45 C. and about 1 C. In the production of theall skin type filaments, the temperature of the spinning bath is notcritical, however, as is well known in the conventional practice in.

the art, certain of the physical properties such as tensile strengthvary directly with the temperature of the spinning bath. Thus, in theproduction of filaments for tire cord purposes in accordance with themethod of this invention, the spinning bath is preferably maintained ata temperature between about 55 C. and 65 C. so as to obtain the desiredhigh tensile strength.

The acid content of the spinning bath is balanced against thecomposition of the viscose. The lower limit of the acid concentration,as is well known in the art, is just above the sl'ubbing' point, thatis, the concentration at which small. slubs of u'ncoagulated viscoseappear in the strand as it leaves the spinning bath. For commercialoperations, the acid concentration of the spinning bath is generallymaintained about 0.4% to 0.5% above the slubbing point. For any specificviscose composition, the acid concentration of the spinning bath must bemaintained above the slubbing point and below the point at which theneutralization of the caustic of the viscose is sufiiciently rapid toform a filament having a skin and core.

' There is a maximum acid concentration for any specific viscosecomposition beyond which the neutralization is sufficiently rapid toproduce filaments having a skin and core. For example, in general, theacid concentration of the spinning baths which are satisfactory for theproduction of the all skin products from a 7% cellulose, 6% causticviscose and containing monoaminopyridine lies between about 6% and about8.4%. The acid concentration may be increased as the amount ofmonoaminopyridine is increased and also as the salt test of the viscoseis increased. There is an upper limit, however, for the acidconcentration based upon the amount of monoarninopyridine and theconcentration of caustic in the viscose. All skin products cannot beobtained if the acid concentration is increased above the maximum valuealthough the amount of monoaminopyridine is increased beyond about 2.5%to 3% while other conditions are maintained constant. Increasing thecaustic soda content of the viscose beyond about 8% is uneconomical forcommercial production methods. For example, a viscose containing about7% cellulose, about 6.5% caustic soda, about 36% (based on the weight ofcellulose) carbon disu'lfi'de', 1% (based onthe weight of cellulose) ofmonoarninopyridine and having a salt test of about 9 when extruded intospinning baths containing 16 to 20% sodium sulfate, 4 to 8% zinc sulfateand sulfuric acid not more than about 8.5%, results in the production ofall skin filaments. Lesser amounts of sulfuric acid may be employed.Greater amounts of sulfuric acid result in the production of productshaving skin and core. A lowering of the amount of monoaminopyridine, thelowering of the caustic soda content or the lowering of the salt test ofthe viscose reduces the maximum permissible acid concentration for theproduction of all skin filaments. It has been determined that themaximum concentration of acid which is permissible for the production ofall skin products is about 9%.

The presence of the monoaminopyridine in the viscose retards theregeneration and, therefore, the amount of monoaminopyridine employedmust be reduced at high :spinning speeds. 'Thus, for optimum physicalcharacteristics of an all skin yarn formed from a viscose as above andat a spinning speed of about 50 meters per minute, the adduct isemployed in amounts Within the lower portion of the range, for example,about 1%. The determination of the specific maximum and optimum.concentration of acid for any specific viscose, spinning bath andspinning speed is a matter of simple experimentation for those skilledin the art. The extruded viscose must, of course, be immersed ormaintained in the spinning 7 bath for a period sufficient to effectrelatively cor'nplete coagulation of the viscose, that is, thecoagulation must .-,be suiiicient so that the filaments wi l no a he 9each.

. 4 other as they are brought together and withdrawn from the bath.

In the production of filaments for such purposes as the fabrication oftire cord, the filaments are preferably stretched after removal from theinitial coagulating and regenerating bath. From the initial spinningbath, the filaments may be passed through a hot aqueous bath which mayconsist of hot water or a dilute acid solution and may be stretched fromabout 70% to 120%, preferably between and Yarns for other textilepurposes may be stretched as low as 20%. The precise amount ofstretching will be dependent upon the desired tenacity and otherproperties and the specific type of product being produced. It is to beunderstood that the invention is not restricted to the production offilaments and yarns but it is also applicable to other shaped bodiessuch as" sheets, films, tubes and the like. The filaments may then bepassed through a final regenerating bath which may contain from about 1%to about 5% sulfuric acid and from about 1% to about 5% sodium sulfatewith or without small amounts of zinc sulfate if regeneration has notpreviously been completed;

The treatment following the final regenerating bath, or the stretchingoperation where regeneration has been completed, may consist of awashing step, a desulfurizing step, the application of a finishing orplasticizing material and drying before or after collecting, or mayinclude other desired and conventional steps such as bleaching and thelike. The treatment after regeneration will be dictated by the specifictype of shaped body and the proposed use thereof.

Regenerated' cellulose filaments prepared from viscose containing thesmall amounts of monoaminopyridine and spun in the spinning baths oflimited acid content have a smooth or non-crenulated surface and consistsubstantially entirely of skin. Because of the uniformity of structurethroughout the filament, the swelling and staining characteristics areuniform throughout the cross-section of the filament. Filaments producedpursuant to this invention and consisting entirely of skin have a hightoughness and a greater flexing life than filaments as producedaccording to prior methods which may be attributed by the uniformity inskin structure throughout the filament. Although the twisting ofconventional filaments, as in the production of tire cord, results in anappreciable loss of tensile strength, there is appreciably less loss intensile strength in the production of twisted cords from the filament'sconsisting entirely of skin. Filaments prepared from viscose containingthe monoaminopyridine have superior abrasion and fatigue resistancecharacteristics and haye' ahigh flex-life as compared to normalregenerated cellulose filaments. Such filaments are highly satisfactoryfor the production of cords for the reinforcement of rubber productssuch as pneumatic tire casings, but the filaments are not restricted tosuch uses and may be used for other textile applications.

Like improvements in the characteristics and properties of the productsare also obtained by incorporation of the monoam'inopyridine in thespinning bath in place of adding it to the viscose. It is essential thatthe composition of the spinning bath, particularly the acidconcentration be maintained within the limits set forth hereinbefore. Inorder to produce products consisting of all skin, the amount ofmonoaminopyridine dissolved in the spinning bat-h must be at least about0.01% by weight and is preferably maintained between about 0.05% andabout 011%. The upper limit of the amount added to the spinning bath. isdependent upon economic considerations since amounts exceeding about0.1% are not more effective in improving the properties of the products.

It is obvious that monoaminopyridine may be added to both the viscoseand the spinning bath, if desired. In

ning bath, and; the composition of the spinning bath S within the statedlimits. The all skin product s of improved properties are obtained onlywhen the spinning operation in the presence of monoaminopyridine iscarried out within the spinning bath composition as set forthhereinbefore.

The invention may be illustrated by reference to the preparation ofregenerated cellulose filaments from a viscose containing about 7%cellulose, about 6.5% caustic soda, and having a total carbon disulfidecontent of about 36% based on the weight of the cellulose. The viscosesolutions were prepared by xanthating alkali cellulose by theintroduction of 36% carbon disulfide based on the weight of thecellulose and churning for about 2 /2 hours. The viscose was thenallowed to ripen for about 30 hours at 18 C. In those instances wherethe modifier was incorporated in the viscose, the desired amount ofmonoaminopyridine was added to the solution and mixed for about 36 hourbefore allowing the viscose to ripen.

Example 1 Approximately 1% 2-aminopyridine (based on the weight of thecellulose) was added to and incorporated in the viscose as describedabove. The viscose employed in the spinning of filaments had a salt testof 9.1. The viscose was extruded through a spinneret to form a 200denier, 120 filament yarn at a rate of about 43 meters per minute. Thecoagulating and regenerating bath was maintained at a temperature ofabout 60 C. and contained 8.3% sulfuric acid, 8% zinc sulfate and 17%sodium sulfate. The yarn was stretched about 74% while passing through ahot water bath maintained at 95 C. The yarn was collected in a spinningbox, washed free of acids and salts and dried.

The individual filaments have a smooth, non-crenulated exterior surfaceand consist entirely of skin, no core being detectable at highmagnification (e.g. 1500 The filaments of a control yarn spun with thesame viscose but without the addition of the modified agent and spununder the same conditions, exhibit a very irregular and serrated surfaceand are composed of about 60% to 70% skin and the balance core with asharp line of demarkation between the skin and core. Other physicalproperties are set forth in the table which follows the examples.

Example 2 A viscose solution as described above (no modifier added)having a salt test of 9.2 was spun into a 210 denier, 120 filament yarnby extrusion into a spinning bath containing 8.1% sulfuric acid, 8% zincsulfate, 19% sodium sulfate and 0.05% 2-aminopyridine. The bath bath wasmaintained at 60 C. and the extrusion rate was about 22 meters perminute. The filaments were passed through a hot water bath maintained atabout 95 C. and stretched about 82%. The yarn was collected in aspinning box, washed free of acid and salts and dried.

The filaments have a smooth, non-crenulated surface and consist entirelyof skin while control filaments have a very irregular and serratedsurface and consist of about 60% to 70% skin and the balance core with asharp line of demarkation between the skin and core. Other physicalcharacteristics are set forth in the table which follows the examples.

Example 3 To a viscose as described above, there was added 1%2-aminopyridine. The viscose had a salt test of 9.2 and was spun into a210 denier, 120 filament yarn by extrusion into a spinning bathcontaining 8.3% sulfuric acid, 8% zinc sulfate, 17% sodium sulfate, andabout 0.05% Z-aminopyridine. The bath was maintained at 60 C. and theextrusion rate was about 22 meters per minute. The filaments weresubsequently passed through a hot water bath at 95 C. and stretchedabout 82%. The yarn was collected in a spinning box, washed free ofacids and salts and dried.

. t 6 The individual filaments were readily distinguishable from controlfilaments in that they have a smooth, noncrenulated surface and consistentirely of skin while the control filaments have a ,very irregular andserrated surface and consist of about 60% to 70% skin and the balancecore with a sharp line of demarkation between the skin and the core.Other physical properties are set forth in the table which follows theexamples.

Example 4 As a control for the foregoing examples, a viscose solution,prepared as described above, having a salt test of 9.2 was spun into a210 denier, 120 filament yarn by extrusion into a bath containing 7.9%sulfuric acid, 8% zinc sulfate and 20% sodium sulfate. The bath wasmaintained at a temperature of about 60 C. The extrusion rate was about22 meters per minute. The water bath was maintained at a temperature ofabout 95 C. and the filaments were stretched 82% while passing throughthe hot water. The yarn was collected in a spinning box, washed free ofacid and salts and dried.

The individual filaments have a very irregular and serrated surface andconsist of about 60% to 70% skin and the balance core with a sharp lineof demarkation between the skin and the core. Other characteristics areset forth in the table which follows:

Tenacity, Grams per denier Elongation, percent Skin, percent Wet Dry WetDry Example 1 Example 2- Example 3 Example 4 (Control) Although thetenacity and elongation are the only properties set forth, they havebeen chosen because of the ease and simplicity with which suchproperties may be determined. In some instances, products made inaccordance with this invention do not exhibit. large or greatimprovements in tenacity and elongation, however, the products consistof a smooth-surfaced, all skin structure and possess improved abrasionresistance, flex-life and other properties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses of itsrelatively high cross-sectional swelling when wet with water, thisswelling amounting to from about 65% to about for rayon produced byconventional methods. Rayon filaments produced in accordance with themethod of this invention have an appreciably lower cross-sectionalswelling characteristic, the swelling amounting to from about 45% toabout 60%.

The monoaminopyridine may be added to any desired viscose such as thosenormally used in industry, the specific viscose composition set forthabove, being merely for illustrative purposes. The monoaminopyridine maybe added at any desired stage in the production of the viscose and maybe present in the cellulosic raw material although it may be necessaryto adjust the amount present to produce a viscose having the properproportions of the adduot at the time of spinning.

The term skin is employed to designate that portion of regeneratedcellulose filaments which is permanently stained or dyed by thefollowing procedure: A microtome section of one or more of the filamentsmounted in a wax block is taken and mounted on a slide with Meyersalbumin fixative. After dewaxing in xylene, the section is placed insuccessive baths of 60% and 30% alcohol for a few moments each, and itis then stained in 2% aqueous solution of Victoria Blue BS conc.(General Dyestuffs Corp.) for 1 to 2 hours. At this point, the entiresection is blue. By rinsing the section first in distilled water andthen in one or more baths composed of 10% water and dioxane for a periodvarying from 510 320 mingtes depending on the panticular filament, thedye is entixely re'movedfrom the cope, leaving ,it restricted to theskin ncas.

Ih i s application is a division of my copendjng application .Serial No;518.932, filed June 29, 1955, now US. Raten No.2,. 1 8- ;Whi-legrefemred embodiments of the inve nti e n have been disclosed, thedescription ,is intended .t be illustrative and it is to be understoodthat changes and variations may be made without'd'eparting from thespirit and sejope 0f the invention as defined by the appendedelaim.

.8 I l im; v v Y A yiscqs e pin, 'ng solution containing fnpm about 0-79 about 3%, based on he eigh of the cellulose in itheyiscose, piampnoamin pyridiner q Refieyences Cited in the file of this patent:U-NHEED STATES PATENTS

